One way of characterizing the cleaning performance of a vacuum cleaner is by reference to its so-called ‘pick-up’ performance: the ability of the vacuum cleaner to pick up dirt and debris from a floor surface. A desirable pick-up performance often includes the ability to pick up both fine dirt as well as so-called ‘large debris’ such as, for example, certain pet snacks, breakfast cereals, grains of rice etc.
Some suction nozzles are provided with a ‘large debris path’, in addition to the main suction opening, which is designed to allow large debris to be drawn into the suction nozzle with reduced clogging or ‘snowploughing’. However, air entering the suction nozzle through the large debris path means that the suction at the main suction opening is reduced. Pickup performance outside of large debris pickup may therefore be reduced. Some suction nozzle designs allow the large debris path to be closed when not needed, in order to mitigate this effect. However, the low pressure inside the suction nozzle with the large debris path closed can cause the suction nozzle to ‘limpet’—sucking itself down onto a floor surface and therefore being difficult to manoeuvre. This effect could be combatted by including a ‘bleed’ path. This provides an additional route for air to be sucked into the suction nozzle, increasing the pressure within the suction nozzle and thereby reducing the chance that it will limpet. However, the provision of an additional route for air into the suction nozzle would further reduce suction at the main suction opening and thus potentially reduce overall performance.